During the process of reservoir fracturing modifaction, several key technical problems need to be solved urgently in Xinjiang oilfield reservoir development, such as difficulties of breaking gum in guar gum fracturing fluid system under low temperature, and poor effect of reservoir modification. To solve these problems, Microbial Enhanced Oil Recovery technique was applied in guar gum fracturing fluid in the present study. The oil sludge was collected from the Shaofanggou group in Ji 7 block of Xinjiang Oilfield, and a strain, named XJ-21, that is capable of producing high-yield surfactant was obtained after enrichment culture, isolation and screening. This strain was identified as Bacillus subtilis according to its morphological, Gram staining and 16S rRNA sequence analysis. The structure of bio-surfactant in XJ-21 strain metabolites was characterized was a substance that is consistent with the structure of the lipid peptide after Fourier transform infrared spectroscopy (FT-IR) analysis. After combination of the XJ-21 strain with an exogenous strain ZW-027, the compound system has wide adaptability to reservoir environment. Under the conditions from 35~55 ℃, not only the jelly guar gum could be broken, but also the viscosity of crude oil in Xinjiang could be reduced. And the viscosity reduction rate reached 95.45% at 50 ℃ in the presence of compound system and the displacement efficiency can be increased by 10.14% on the basis of water flooding.